1. Field of the Invention
The present invention relates to a belt feeding device for rotating an endless belt member such as a recording sheet feeding belt or a photosensitive belt in a color image forming apparatus or the like, and more particularly to an improvement in such a belt feeding device having means for preventing meander of the endless belt member.
2. Description of the Related Art
Such a belt feeding device having means for preventing meander of the endless belt member is known from Japanese patent Laid-open No. Hei 5-319611, for example.
In the belt feeding device, the belt member is wrapped around a driving roll and a plurality of driven rolls, and is circularly moved at a given speed by rotating the driving roll. One of the driven rolls is used as an edge guide roll for guiding a side edge of the belt member, thereby preventing meander of the belt member.
FIG. 7 shows the edge guide roll and its peripheral equipment. Referring to FIG. 7, reference numeral 50 denotes the edge guide roll; reference numeral 51 denotes the belt member adapted to be moved in the direction shown by an arrow A; and reference numeral 52 denotes an edge guide mounted in the vicinity of one axial end of the edge guide roll 50. The edge guide 52 is movable in the axial direction of the edge guide roll 50 (i.e., the direction shown by an arrow B), and is biased to the belt member 51 by means of a spring 53. The spring 53 is provided with an adjuster mechanism 54 for freely adjusting a biasing force of the spring 53.
As shown in FIGS. 7 and 8, the edge guide roll 50 is an elastic roll formed by axially arranging a plurality of disklike elastic fins 50a on the outer circumferential surface of a rotating shaft 50b. The elastic fins 50a at the same axial position on the rotating shaft 50b are equally spaced in the circumferential direction of the rotating shaft 50b. Further, the edge guide roll 50 is inclined at a slight angle to the driving roll (not shown) so that when the belt member 51 is rotated, it is always offset to the edge guide 52 in the axial direction of the edge guide roll 50 (this offset will be hereinafter referred to as belt walk).
Accordingly, the belt member 51 is rotated in such a manner that a side edge 51a thereof always slides on the edge guide 52. At this time, the biasing force of the edge guide 52 is adjusted to balance a force of offset of the belt member 51 to the edge guide 52 (this force of offset will be hereinafter referred to as a walk force), thereby completely canceling the belt walk of the belt member 51.
Such forcible stop of the belt walk of the belt member 51 by the edge guide 52 causes a reaction of the walk force against the side edge 51a of the belt member 51 sliding on the edge guide 52 (this reaction will be hereinafter referred to as an edge force), and it is considered that the side edge 51a of the belt member 51 may be damaged (buckled, cracked, etc.) by the edge force. However, since the elastic roll is used as the edge guide roll 50 in this belt feeding device as mentioned above, the elastic fins 50a of the edge guide roll 50 are elastically deformed in the axial direction of the edge guide roll 50 upon application of the edge force to the side edge 51a of the belt member 51, thereby reducing the edge force applied to the side edge 51a. Accordingly, although the belt walk of the belt member 51 is forcibly stopped by the edge guide 52, the damage to the side edge 51a of the belt member 51 can be prevented.
Further, the above-cited literature also discloses an embodiment wherein no angular difference in arrangement between the edge guide roll and the driving roll is given, but a pair of edge guides are provided at both side edges of the belt member.
The elastic roll is conventionally manufactured by performing injection molding of a soft material such as rubber or synthetic resin to form the elastic fins 50b projecting from the outer circumferential surface of the rotating shaft 50a, and then grinding or cutting the outer circumferential surface of each elastic fin 50b by moving a tool from one axial end to the other axial end of the rotating shaft 50a to thereby finish the outer circumferential surface of each elastic fin 50b to a given outer diameter.
As mentioned above, the outer circumferential surface of each elastic fin 50b is ground or cut by moving the tool from one axial end to the other axial end of the rotating shaft 50a in finishing the outer circumferential surface of each elastic fin 50b to the given outer diameter according to this manufacturing step for the elastic roll. Accordingly, each elastic fin 50b is deformed in the same direction as the direction of movement of the tool during the finishing step. As a result, the outer circumferential surface of each elastic fin 50b is taperingly ground or cut by the tool as shown in FIG. 9.
Accordingly, when the belt member 51 is wrapped around this elastic roll manufactured by the above method to construct the belt feeding device, each elastic fin 50b is pressed to be deformed by the belt member 51 as shown in FIG. 10 and resultantly acts to move the belt member 51 in such a direction as to cancel this deformation. That is, each elastic fin 50b generates a walk force acting on the belt member 51 in the direction shown by an arrow C in FIG. 10 opposite to the direction of movement of the tool that finished the outer circumferential surface of each elastic fin 50b to the given outer diameter, thus generating the belt walk. As a result, the edge force acting from the edge guide 52 to the side edge 51a of the belt member 51 is increased to reduce the effect of the elastic roll intended to reduce the edge force.